First of a very successful line of integrated amplifiers which would receive many awards and sell very well worldwide. Designed and produced before the Alpine "takeover / collaboration" and just before the DAD revolution, the L-550 did receive a "State of the Art" award in 1982 besides being selected as "Best Product" by Stereo Sound. Most of the direct followers also became Stereo Sound "Best Product" : L-550X, L-560 and the successful L-540 and L-570. All are versions of the same basic circuit : Single-Stage amplification, Duo-ßeta, plus-X, Circuit /S and Class A all the way, real hot Class A. All did also sport something which was not to be discarded once the fad faded : double Heat-Pipes !

The necessary Heat-Pipes have vents top and bottom of the enclosure : 2x 50W of pure Class A produces heat, especially when idling current is to be set at 160mV for each channel ! The pre-Heating switch is used to get the L-550 reach its cruising speed while the power-on button is off ; current is cut from the final transistors but heats-up the rest of the circuit.

Single-Stage amplifier As in all contemporary Luxmans, there is no second stage so the 1st stage uses a high Gm low-noise FET (for the MC input) with a 7mA current for the necessary gain. If Duo-ßeta is used as usual in the power-supply, in the L-550, it also was implemented in the EQ phono section - that's Duo-ßeta Circuit /S.

Line level input reach the circuit where the "phono straight" mode starts, the latter bypassing the subsonic, high-cut, monitor and source selectors. Unlike other contemporary LUX amps, the 9-turnover NF tone controls are not placed withing the power amp's main Duo-ßeta loop but the Linear Equalizer which can subtly tilt RIAA frequency response is. The attenuator is a 2-gang 50kOhm pot sourced from, as always and for nearly everybody, ALPS, aka Alpine :)